This invention relates to a method for treating agricultural soil with sewage sludge ash in admixture with water treatment lime so as to enhance the nutrient value and raise the pH of the soil for improved plant growth, while simultaneously minimizing the risk of wind blown ash dust.
The incineration of sewage sludge has been done for decades with the resulting ash presenting a disposal problem. Although its limited application on agricultural soil for its nutrient value (e.g., plant-available phosphorus and potassium and multiple trace elements or micronutrients), has heretofore been recognized, it has not received any widespread use as a soil conditioner. Some may say that the phosphorus in it available for plant growth is relatively low; but the plant-available phosphorus in it is sufficient to be meaningful for plant growth. Not insignificant is its fine particle size, down to even less than a micron. It dries readily even when applied as a liquid or a paste; and its extremely fine particles are easily wind driven. It must be worked into the soil relatively quickly after application; the relatively quick tillage requirements for land applied sewage sludge itself (for reasons of the stench as well as concerns of wind blown dust on drying) have been considered equally applicable to the ash. Thus, maintaining reliable relatively uniform land coverage of it in a windy environment has made it relatively unattractive to work with as an agricultural soil conditioner.
Water treatment lime, that is, the lime by-product of municipal water softening operations, also has been for decades a waste product. For years it was considered useless. However, it has over the past several years received attention as a soil conditioner, especially for raising the pH of acid soils. As such it has been employed with success and with convenient maintenance of relatively uniform land coverage even in windy environments, largely because of its relatively strong tendency to retain or attract water and also because of its relatively sand particle size when dry.
Both waste products, namely the sewage sludge ash and the water treatment lime, have presented environmental concerns for decades. Despite the fact that each heretofore has been separately proposed for use on agricultural soil, with application of water treatment lime on agricultural soil being now a readily accepted practice, no one insofar as known has heretofore proposed or recognized the unique benefit of combining these waste products to solve the vexing problems associated with tonnage scale land application of sewage sludge ash. It is to a solution of those vexing problems that this invention is directed.